The present invention relates to an outboard engine system including an engine having a crankshaft disposed vertically and a cylinder axis disposed longitudinally.
In general, an outboard engine system includes a body frame on which an engine is mounted, and which is detachably mounted to a hull through a mounting bracket. The engine is mounted vertically on the body frame with a crankshaft facing vertically and with a cylinder axis facing longitudinally, so that the transmission of a power to a drive shaft disposed vertically within the body frame can be conducted easily.
The vibration generated by the operation of the engine is transmitted from the body frame through the mounting bracket to the hull, but to reduce the vibration, the body frame is supported on the mounting bracket through an elastomeric member. A thrust generated by a propeller of the outboard engine system is transmitted from the body frame through the elastomeric member to the mounting bracket and further transmitted from the mounting frame to the hull. Therefore, it is required that the elastomeric member should meet conflicting demands that the thrust generated by the propeller is transmitted effectively from the body frame to the mounting bracket, while the transmission of the vibration from the body frame to the mounting bracket is reduced effectively.
One of techniques for meeting the demands is to reduce the vibration itself generated by the engine. For example, in a 2-cylinder and 4-cycle engine, it is common that two pistons are disposed at the same crank phase, and the ignition is conducted at equal intervals with ignition timings displaced by 360xc2x0. To reduce the primary vibration generated by the engine, an outboard engine system has been proposed in Japanese Patent Application Laid-open No.63-192693, in which the rotational mass of counterweights of the crankshaft relative to the reciprocation mass of the piston is determined at 50%, and a balancer shaft reversed at the same speed as the crankshaft has the remaining 50%.
Another technique for meeting the demands is to ensure that the rigidity of the elastomeric member supporting the body frame to the mounting bracket has an anisotropy. Thus, an outboard engine system has been proposed in Japanese Patent Application Laid-open No.2-37096, wherein the rigidity of an elastomeric member is set to be large in a direction to transmit a thrust generated by a propeller to a hull (i.e., in a longitudinal direction) and small in a direction perpendicular to such direction (i.e., in a lateral direction), thereby preventing the transmission of the lateral vibration to the hull, while permitting the thrust to be transmitted effectively to the hull.
However, the outboard engine system described in Japanese Patent Application Laid-open No.63-192693 suffers from not only a problem that it is necessary to add a special balancer device and hence, the weight and the cost are increased, but also a problem that a power transmitting system such as a gear for driving a balancer shaft in operative association with a crankshaft generates a noise.
The outboard engine system described in Japanese Patent Application Laid-open No.2-37096 suffers from the following problem: The elastomeric members are disposed at two points on opposite sides of a vertical axis (a torque rolling axis) extending through the center of gravity of the engine, so that a torque reaction generated in the crankshaft with the operation of the engine can be supported. For this reason, the positions of the elastomeric members are at a central portion of the outboard engine system and are liable to interfere with other equipments. This is inconvenient in respect of the layout.
The present invention has been accomplished with the above circumstances in view, and it is an object of the present invention to provide an outboard engine system, wherein a thrust generated by a propeller can be transmitted effectively to a hull, while effectively reducing the transmission of the vibration generated by an engine.
To achieve the above object, according to the present invention, there is provided an outboard engine system comprising a system body, an engine mounted on the system body, a mounting means detachably mounted to a hull, and a mount device having a pair of left and right elastomeric members for supporting the system body on the mounting means, characterized in that the engine is disposed, so that a crankshaft is disposed vertically, and a cylinder head disposed to face rearwards with a cylinder axis disposed in a longitudinal direction parallel to a propeller shaft, and so that a rate of balance between the reciprocal inertia mass of a piston and a rotational inertia mass of the crankshaft is set at approximately 100%; the elastomeric members are disposed on left and right opposite sides of the engine, and the rigidity of the mount device is set so that the rigidity in a tangent direction about a phantom center point of vibration in a high rotational speed range of the engine is lower than the rigidity in a radial direction about the phantom center point of vibration.
With the above arrangement, a longitudinal inertia force generated by the reciprocal inertia mass of the piston is converted into a lateral inertia force by the rotational inertia mass of the crankshaft. The lateral inertia force vibrates the system body having the engine mounted thereon laterally about the phantom center point of vibration. At this time, the rigidity of the mount device having the elastomeric members disposed on left and right opposite sides of the engine to resiliently support the system body on the mounting means mounted on the hull is set, so that the rigidity in the tangent direction about the phantom center point of vibration is set to be lower than the rigidity in the radial direction about the phantom center point of vibration and hence, the lateral vibration about the phantom center point of vibration can be reduced effectively due to the low rigidity of the mount device to improve the riding comfort on the hull. A thrust acting in the longitudinal direction parallel to the propeller shaft is transmitted to the hull through the mount device, but the rigidity of the mount device in the direction of the thrust is set at a high value and hence, the thrust can be transmitted effectively to the hull due to the high rigidity of the mount device.
In addition to the above arrangement, there is also provided an outboard engine system, wherein an angle formed by a straight line extending forwards from the phantom center point of vibration with a straight line extending from the phantom center point of vibration toward the elastomeric member is smaller than 45xc2x0.
With the above arrangement, the angle formed by the straight line extending forwards from the phantom center point of vibration with the straight line extending from the phantom center point of vibration toward the elastomeric member is smaller than 45xc2x0. Therefore, the deviation between the direction of the thrust (the direction of the straight line extending forwards from the phantom center point of vibration) and the direction in which the rigidity of the mount device is highest (the direction of the straight line extending from the phantom center point of vibration toward the elastomeric member) can be decreased, whereby the thrust can be transmitted further effectively to the hull.
According to the present invention, there is provided an outboard engine system comprising a system body, an engine mounted on the system body, a swivel shaft for pivotally supporting the system body on a hull, a mount arm integral with the swivel shaft, a mount device having a pair of left and right elastomeric members for supporting the system body on the mount arm, and a steering handlebar connected to the mount arm to swing the system body about the swivel shaft, characterized in that the engine is disposed, so that a crankshaft is disposed vertically, and a cylinder head is disposed to face rearwards with a cylinder axis disposed in a longitudinal direction parallel to a propeller shaft, and so that a rate of balance between the reciprocal inertia mass of a piston and a rotational inertia mass of the crankshaft is set at approximately 100%; the elastomeric members are disposed on left and right opposite sides of the engine; the rigidity of the mount device is set so that the rigidity in a tangent direction about a phantom center point of vibration in a high rotational speed range of the engine is lower than the rigidity in a radial direction about the phantom center point of vibration; and the swivel shaft is disposed on an arc of a circle extending through the elastomeric members about the phantom center point of vibration.
With the above arrangement, a longitudinal inertia force generated by the reciprocal inertia mass of the piston is converted into a lateral inertia force by the rotational inertia mass of the crankshaft. The lateral inertia force vibrates the system body having the engine mounted thereon laterally about the phantom center point of vibration. At this time, the rigidity in the mount device having the elastomeric members disposed on the left and right opposite sides of the engine to resiliently support the system body on the hull is set, so that the rigidity in the tangent direction about the phantom center point of vibration is lower than the rigidity in the radial direction about the phantom center point of vibration and hence, the lateral vibration about the phantom center point of vibration can be reduced effectively due to the low rigidity of the mount device to improve the riding comfort on the hull. A thrust acting in the longitudinal direction parallel to the propeller shaft is transmitted to the hull through the mount device, but the rigidity of the mount device in the direction of the thrust is set at a high value and hence, the thrust can be transmitted effectively to the hull due to the high rigidity of the mount device. Moreover, the swivel shaft is disposed on the arc of the circle extending through the elastomeric members about the phantom center point of vibration and hence, the mount arm can be prevented from being swung about the swivel shaft by the vibration transmitted through the mount device to the mount arm, thereby suppressing the transmission of the vibration to the steering handlebar connected to the mount arm to the minimum.
In addition to the above arrangement, there is provided an outboard engine system, further including a cover member fastened to a rear surface of a lower end of an extension case connected to the system body to define a space with a horizontal section closed, and a mount block which is mounted at a lower end of the swivel shaft and retained in the space.
With the above arrangement, a box-shaped structure of a high rigidity with the horizontal section closed is provided by fastening the cover member to the extension case and hence, the mount block can be firmed retained within the structure to effectively prevent the generation of resonance.
Meanwhile, an engine-supporting block 41 in an embodiment corresponds to the system body of the present invention; a mounting bracket 55 in the embodiment corresponds to the mounting means of the present invention; an upper mount 65 in the embodiment corresponds to the mount device of the present invention; an upper mount rubber member 74 in the embodiment corresponds to the elastomeric member of the present invention.